1. Field of the Invention
This invention relates to liquid chromatography and its use for determining the oligomeric content of prepolymers and polymers. More particularly, it relates to a reversed-phase, high-performance liquid chromatographic method for the monitoring of the oligomeric content in polyethylene terephthalate prepolymer and polymer.
2. Description of the Prior Art
In German Democratic Republic Patent No. 214,693, Bogatzki et al., disclosed a quantitative liquid chromatographic process for the determination of oligomers in polyalkylene terephthalates. Reversed-phase chromatography was used to quantify the levels of oligomers in polyethylene terephthalate and polybutylene terephthalate samples. According to the method, previously known solution and elution systems, such as fluorinated alcohols with a specific water content, which dissolved the alkylene terephthalate molecules but allowed all molecules to pass through a UV detector and included the absorption of all molecules in the analysis, were used; the UV absorption of all alkylene terephthalate molecules was equated, resulting in the area of the peak(s) corresponding to the mass fraction and the peak identification being performed on the basis of synthesis of an oligomer series, and the influence of end group reactions on the location of the peaks was noted.
In Japanese Kokai Tokkyo Koho 81 12,551, Teijin Ltd. disclosed the injection of a polyester solution in a fluorine-containing alcohol, such as hexafluorisopropanol, and chloroform into a gel permeation chromatographic column and elution with chloroform to determine molecular weight distribution accurately.
In Japanese Kokai Tokkyo Koho Japan 62,116,257 (87,116,257), Kanzaki, et al, disclosed that polyethylene terephthalate may be analyzed with good reproducibility by dissolving the polyesters or their oligomers in mixtures of chloroform and hexafluoroisopropanol and fractionating by gel permeation chromatography with elution by mixtures of chloroform with hexafluoroisopropanol and ethylene glycol.
From time to time, it becomes necessary to ascertain the oligomeric content of a poly(ethylene terephthalate) sample. For example, the presence of dicarboxylic acid-substituted, low-molecular weight oligomers of terephthalic acid and ethylene glycol could be a cause of plugging of spin-pack filters employed in the manufacture of textile yarns from purified terephthalic acid. Such plugging is undesirable, since it results in a process interruption. Knowing the oligomer content of the polyethylene terephthalate sample would be beneficial.
A method has been developed to monitor the prepolymer and the polymer. The method was used to investigate the above problem and was instrumental in showing a definite relationship between oligomer content and filter plugging.